Technical Abstract:
The Soil Conditioning Index (SCI) administered by the USDA-NRCS predicts the consequences of tillage practices and cropping systems on trends in SOC but does not represent an actual quantity or accumulation rate of SOC. We calibrated the EPIC model for three major land resource areas in the southeastern USA based on sensitive model parameters and five to ten years of measured soil organic carbon (SOC) data from each location to simulate the effects of conventional (CT) and conservation (NT) tillage practices in cotton and corn production systems on SOC storage and accumulation rates, and to develop a relationship between EPIC-predicted and SCI-predicted SOC. Our results show that EPIC-predicted 50-y SOC would increase with both CT and NT practices with a wheat cover crop in the Texas Blackland Prairie, with CT and manure fertilizer in the Alabama Coastal Plain, and with CT and a wheat cover crop in Mississippi. The SOC would decrease after 50 years in CT and NT with a wheat cover crop and mineral fertilizer in Alabama, and stabilize near its original value with NT and manure fertilizer. The SOC under NT with a wheat cover crop in Mississippi would decrease below its initial value. We will simulate SOC for other locations in the southeastern USA with the calibrated model and develop the relationship between 50-y SOC predictions using the SCI at the same sites. The rate and quantity of SOC accumulation over time could be important for farmers and policymakers in future global carbon trade markets.